- Students will be able to
- locate the seeds within a mature plant's seed heads
- count the seeds within sample heads and use averages to estimate the total number of seeds a plant produces
- understand how quickly a plant or weed can multiply, and the benefits and problems this represents.
- Locate plants or weeds that are in seed. Ones with distinct seed heads or pods are best.
Examples of plants to use
What You Will Need:
- Student access to seeding plants or weeds (in a garden, wild area, or on a farm).
- Trays or plates for sorting and counting seeds on.
- Optional: Artist's paint brush or similar for sorting and counting small seeds.
- Optional: Magnifying glass for close inspection of seeds.
Many types of plants use seeds to reproduce. For this activity you will be counting the seeds that a plant produces to work out how many offspring it could yield under perfect conditions. In nature, perfect conditions don't exist, but in farming and gardening most seeds survive to adulthood.
What to do
Choose your plant
- Find a plant or weed with mature, drying seed heads. Good options are wheat plants and dandelions.
- If the plant hasn't got too many seeds then carefully count and record all its seeds.
If the plant has many seed heads:
- Choose one seed head from the plant and break it apart, spreading the seeds into a tray.
- Carefully count and record the number of seeds. (Tiny seeds may be easier to sort into piles of 10 at a time using a small paint brush or similar.)
- Repeat this count for some other seed heads from the same plant, trying not to choose the biggest or smallest heads every time.
- Find the average (mean) number of seeds in a head. (Hint: This is the total number of seeds divided by the number of heads you counted. Example: If there is a total of 75 seeds in 3 heads, then the average is 75 divided by 3 = 25.)
- Count how many seed heads there are in total on the plant, then work out the estimated total number of seeds on the plant. (Hint: Number of seed heads x average number of seeds per head = estimated total.)
- Repeat the process for other types of plants.
What I found
- Make a data table to show your results for the range of plants you counted.
- Under perfect conditions what could one seed multiply up to by the next generation? Give examples.
- Some plants like dandelions keep producing seeds over a very long time. How would this affect your results?
Plants and weeds in the wild
- Why won't all the seeds that a plant or weed produces survive in the wild?
Plants in the garden or on the farm
- How does a gardener or farmer improve the chances of seeds surviving and growing into mature plants?
Applying your knowledge
- There is an old saying about managing weeds in a garden, "One year's seeding, seven years of weeding." What does this mean? How does this relate to good and bad weeding practices?
- How could a farmer estimate the yield of their wheat crop before harvesting it?
Picture credits: All photos (Copyright Peter E. Smith, NSIL).